Double gate planar field effect transistors

ABSTRACT

A transistor device includes multiple planar layers of channel material connecting a source region and a drain region, where the planar layers are formed in a stack of layers of a channel material; and a gate conductor formed around and between the planar layers of channel material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application of co-pending U.S. patentapplication Ser. No. 13/161,013 filed on Jun. 15, 2011, incorporatedherein by reference in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to semiconductor nanowire field effecttransistors (FETs) and, in particular, to vertically stacked nanowiredevices having double gate planar FETs and methods for making the same.

2. Description of the Related Art

Silicon nanowire-based metal oxide semiconductor field effecttransistors (MOSFETs) are of interest due to their superiorelectrostatics. Semiconductor nanowire field effect transistors havebeen fabricated by generating a collection of nanowires and then placingthem where desired (known as a bottom-up approach) or throughlithographic patterning. However, for nanowires with small diameters,achieving the high layout density required for a competitive technologyis challenging. For example, a nanowire field effect transistor (FET)with a body diameter of 10 nm would require a layout pitch of less than32 nm simply to match the channel width density of planar devices.Reducing the body diameter to 5 nm reduces the required pitch to roughly15 nm. This is well beyond the range of what optical lithography cancurrently provide, even with pitch doubling techniques.

Additionally, despite the advantages of nanowires, their small diameteris significantly limiting with respect to current carrying capacity.Furthermore, it can be difficult to form existing nanowire technologieson the same chip with other structures.

SUMMARY

A transistor device includes a plurality of planar layers of channelmaterial connecting a source region and a drain region, wherein theplanar layers are formed in a stack of layers of a channel material; anda gate conductor formed around and between the planar layers of channelmaterial.

An integrated circuit includes a planar device and a nanowire device.The planar device includes a plurality of planar layers of channelmaterial connecting a source region and a drain region, wherein theplanar layers are formed in a stack of layers of a channel material; anda gate conductor formed around and between the planar layers of channelmaterial. The nanowire device includes a plurality of nanowires ofchannel material connecting a source region and a drain region, whereinthe nanowires are formed in a stack of wires of the channel material;and a gate conductor formed around and between the nanowires of channelmaterial.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a diagram that shows nanowires hardmasks and planar hardmaskson the same chip according to the present principles.

FIG. 2 is a diagram that shows stacked layers of channel material andsacrificial material according to the present principles.

FIG. 3 is a diagram that shows a hardmask pattern to produce stackednanowires according to the present principles.

FIG. 4 is a diagram that shows a dummy gate according to the presentprinciples.

FIG. 5 is a diagram that shows sacrificial material around the dummygate according to the present principles.

FIG. 6 is a diagram that shows the removal of the dummy gate to exposeparts of the hardmask according to the present principles.

FIG. 7 is a diagram that shows a fin etch according to the presentprinciples.

FIG. 8 is a diagram that shows removal of the hardmask according to thepresent principles.

FIG. 9 is a diagram that shows formation of sidewalls according to thepresent principles.

FIG. 10 is a diagram that shows removal of sacrificial material to formnanowires according to the present principles.

FIG. 11 is a diagram that shows the formation of a gate according to thepresent principles.

FIG. 12 is a diagram that shows a hardmask to form stacked planesaccording to the present principles.

FIG. 13 is a diagram that shows a dummy gate to establish a planarlocation according to the present principles.

FIG. 14 is a diagram that shows the formation of sacrificial materialover a solid hardmask and the removal of the dummy gate according to thepresent principles.

FIG. 15 is a diagram that shows the removal of the hardmask and theexposure of stacked planar layers according to the present principles.

FIG. 16 is a diagram that shows etched planar layers according to thepresent principles.

FIG. 17 is a diagram that shows a nanowire structure and a planarstructure formed on a single chip.

FIG. 18 is a block/flow diagram that shows an exemplary method forforming stacked nanowire/planar devices according to the presentprinciples.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Vertically stacking nanowires allows for an increase in channel widthlayout density. Meanwhile, a self-aligned gate-to-landing pad structureenables tight gate pitch. Described briefly, the present principlesallow for the creation of small-diameter nanowires arranged in avertical mesh to form a gate-all-around (GAA) field effect transistor(FET). The present principles also provide for planar double-sided FETs.A similar process is employed for both, where the type of device that isproduced may be determined by determining the shape of a hardmask asdescribed below. Relative to the nanowire design, the double-sidedplanar FETs have substantially higher current capacity and lowerthreshold voltages.

Nanowire and planar FETs may be formed according to the presentprinciples using chemical etching. Layers of nanowire material andsacrificial material are alternately layered on top of a substrate.Using a hardmask and a dummy gate to define the positions of channels,sacrificial material may be selectively removed to expose the nanowiresand/or planes. A final gate is then introduced, filling the gaps betweenthe wire or planes. In this manner, vertically stacked nanowires andplanes are produced having a thickness below that which is possibleusing optical lithography. Although only nanowires and planes arediscussed herein, it is contemplated that other structures could beformed using the present principles, based on the shape and size of theapplied hardmask as described below. The present principles also permitfor these structures to be formed simultaneously, using a singleprocess.

It is to be understood that the present invention will be described interms of a given illustrative architecture having a wafer; however,other architectures, structures, substrate materials and processfeatures and steps may be varied within the scope of the presentinvention.

Designs described herein may be part of a design for an integratedcircuit chip. The chip design may be created in a graphical computerprogramming language, and stored in a computer storage medium (such as adisk, tape, physical hard drive, or virtual hard drive such as in astorage access network). If the designer does not fabricate chips or thephotolithographic masks used to fabricate chips, the designer maytransmit the resulting design by physical means (e.g., by providing acopy of the storage medium storing the design) or electronically (e.g.,through the Internet) to such entities, directly or indirectly. Thestored design is then converted into the appropriate format (e.g.,GDSII) for the fabrication of photolithographic masks, which typicallyinclude multiple copies of the chip design in question that are to beformed on a wafer. The photolithographic masks are utilized to defineareas of the wafer (and/or the layers thereon) to be etched or otherwiseprocessed.

Methods as described herein may be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It will be understood that when an element as a layer, region orsubstrate is referred to as being “on” or “over” another element, it canbe directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a chip 102 is shown havingnanowire hardmasks 104 and a planar hardmask 106. By forming both typesof devices on a single chip, each may be employed for its respectiveadvantages.

Referring now to FIG. 2, the formation of stacked layers is shown. Asubstrate may include an insulator layer 201 formed from, e.g., silicon,and a dielectric layer 202 formed from, e.g., silicon oxide (SiO₂). Theinsulator layer 201 and dielectric layer 202 may be grown epitaxially.Channel layers 208 and sacrificial layers 206 may be formed on thedielectric layer 202 and may include, for example, silicon and SiGerespectively. Another dielectric layer 210 may be formed on top and mayinclude, for example, SiO₂. The sacrificial layers 206 may use either n+or p+ doped SiGe. This may be accomplished by, for example, startingwith a silicon-on-insulator (SOI) wafer, thinning the top silicon downto the desired thickness, and then epitaxially growing alternatingcrystalline sacrificial material 206 and channel material 208 on top ofthe thinned silicon. Crystal orientations <1 1 0> and <1 0 0> are shownfor reference. To enable directional etching of a sacrificial materialsuch as SiGe, the starting SOI wafer may be chosen to be of a <1 1 0>crystal orientation. The active regions of the alternating layers 206and 208 are then patterned by, for example, photolithography followed byreactive ion etching (RIE) isolation of active regions from one another.Such isolation may be performed for example by shallow trench isolation(STI), where non-active regions are filled with a dielectric such asSiO₂ to planarize the surface of the substrate 202. Alternatively, mesaisolation may be used where non-active regions are simply etched away.In FIG. 4 below, a device is planarized and employs shallow trenchisolation with a dielectric liner 204 including, e.g., a nitride.

Referring now to FIG. 3, hardmask patterning is shown. The layer 204 anda top layer 210 are etched to form a pattern 302 to specify thepositions of the nanowires. Nanowire mesh (FIG. 10) and stacked planar(FIG. 16) structures may both be formed on the same chip simply bychoosing appropriate hardmasks, as discussed in further detail below.

Referring now to FIG. 4, a dummy gate 404 is shown. After the hardmaskpatterning 302, an etch stop layer 402 may be grown over exposed activeregion to use as an etch stop for the next step. The etch stop layer 402may include, for example, a thin oxide layer. The dummy gate 404 furtherspecifies the positions of the nanowires/planes and also represents theeventual location of the device's gate. The dummy gate 404 may be formedfrom, e.g., poly-silicon plus a silicon nitride hardmask. To enable adirectional etch of, for example, a sacrificial layer 206, the dummygate 404 should preferably be oriented along the <100> direction, asillustrated. Junction engineering to exposed source/drain regions 406may be performed at this point. For example, a top-down implant may beemployed to dope the top layers 208, the source/drain regions 406 may berecessed and implanted with an angled implant, or the source/drainregions 406 may be recessed and then filled in with an epitaxially grownembedded source/drain. Spacers (not shown) formed on the sidewalls ofthe dummy gate 404 could be used for adjusting the distance of thesejunction engineering processes from the channel. For some processes,such as the source/drain 406 recess or embedded source/drain 406 growth,a dummy gate hardmask (not shown) such as SiN should be included as thetop layer of the dummy gate material stack to protect the dummy gate 404during the junction engineering steps.

To form contacts 406 for the devices, sacrificial material 206 may be aconductor or a semiconductor. In the case of a semiconductor (such asSiGe), the sacrificial material 206 may be heavily doped so that it isconductive. In the case of a source/drain 406 formed of heavily dopedsilicon/SiGe layers, current could flow freely through the layers. Inthe case of a recessed source/drain with epitaxially grown embeddedsource/drain regions 406, the source/drain regions 406 would be uniform.Silicide/contact vias would go on top of the source/drain 406 as in anormal complementary metal-oxide semiconductor silicon process flow.

Referring now to FIG. 5, a dielectric fill is shown. Sacrificialdielectric 502 fills in alongside the dummy gate 404 and is thenplanarized. The sacrificial dielectric may include, for example, SiO₂ orother materials.

Referring now to FIG. 6, parts of a fin hardmask pattern 302 are exposedafter the removal of the dummy gate 404. In the case of a planar device,the solid hardmask 1202 (see FIG. 12 below) will be exposed within thesacrificial dielectric 502. The exposed hardmask 302 represents thefinal positions of the nanowires. The dummy gate 404 of FIG. 5 may beremoved using chemical etching or RIE to expose the hardmask 302.

Referring now to FIG. 7, the hardmask pattern 302 is etched down intothe SiGe/silicon stack of alternating layers 206 and 208. This exposesthe layers 206 and 208. The etching may be performed using any suitableprocess.

Referring now to FIG. 8, fins 802 are exposed after an etch processremoves the nitride hard mask pattern 302 of FIG. 7. The top layer 210of SiO₂ remains on channel layers 208 and sacrificial layers 206.

Referring now to FIG. 9, a spacer 902 is formed with a substantialoveretch that clears the sidewalls of exposed fins 802. The spacer 902may include a nitride or other materials. The spacer 902 protects thesidewalls of the fins 802 from subsequent etching.

Referring now to FIG. 10, exposed nanowires 1002 are shown. Thesacrificial layers 208 are removed simultaneously from the nanowiresusing directionally selective etching, for example, with chemicaletching using the above-described materials, with dry etching, or withlow-temperature wet or dry oxidation. This leaves the channel layers 208to form the nanowires 1002. Solid source diffusion annealing is employedto dope the source and drain regions of nanowires 1002. Differentialchemical oxidation may be employed to preferentially oxidize the heavilydoped SiGe of sacrificial layer 208 while forming only an interfaciallayer on the undoped silicon.

Referring now to FIG. 11, a nanowire structure is shown. The device isfilled in with a gate stack 1102 and planarized to form a smoothsurface. The gate stack 1102 may include a dielectric such as SiO₂ orHfO₂, a workfunction setting metal such as TiN or TaN, and then a fillermetal such as Al or W that completely surrounds the nanowires 1002 andfills the space left by the removal of dummy gate 404 in FIG. 6. Due tothe topography of the channels and the narrow space between the channellayers 208, the gate stack material may be deposited with extremelyconformal methods such as low-pressure chemical vapor deposition (LPCVD)or atomic layer deposition (ALD).

Referring now to FIG. 12, an alternative embodiment is shown thatproduces a double-sided gate planar FET. Instead of employing a finpattern 302 shown in FIG. 3, a solid hardmask pattern 1202 is formed byetching the layer 204. The hardmask may include, for example, siliconnitride. The hardmask 1202 is not necessary if only planar devices aredesired, but protects the stacked planar layers from the etch describedabove with respect to FIG. 7. The solid hardmask 1202 protects theunderlying layers 206 and 208.

Referring now to FIG. 13, a dummy gate 1302 is shown disposed over thehardmask 1202. As described above with respect to FIG. 4, the dummy gateestablishes the location of the subsequent planar device.

Referring now to FIG. 14, the formation of sacrificial dielectric fills502 and the removal of the dummy gate is shown. Solid hardmask 1202 isexposed between the fills 502. Also shown is a portion of material 1402at the edge of the solid hardmask 1202 which was not covered. Thisexposed material 1402 will be etched as shown in FIG. 15.

Referring now to FIG. 15, an etch process removes the exposed stackedlayers 206 and 208, as above in FIG. 8, but does not affect the portionsthat were covered by hardmask 1202. The hardmask 1202 is removed toexpose top layer 210. A shelf 1502 permits access for a subsequent etchof the sacrificial layers 206.

Referring now to FIG. 16, a planar gap structure 1602 is shown. Anundercut etch employing, for example, a directionally selective etch, isemployed to remove sacrificial material 206 between the channel layers208, forming gaps 1602. To access the sides of the stacks, the shelf1502 provides an opportunity for the etch to reach the sacrificialmaterial 206. After performing the etch, gate material can be filled inas shown in FIG. 11.

As an example, if a 10:1 directionally selective etch is used, a gatewith a length of 20 nm could be created by starting with a 10 nm trench1502 that allows for a 5 nm expansion on either side. This allows for a50 nm release in the desired direction from both sides, allowing for amaximum “fin width” of 100 nm. In such a structure, it may be assumedthat the bottom layer of silicon 208 is not fully released, such thattwo double-gated silicon channel planes 1604 may be formed on top of onesingle-gated silicon channel plane 1606. This provides an exemplarycurrent carrying area of 5× the layout area. So for example, in a layoutarea of 1 micron with a normal planar device (using, e.g., bulk siliconor silicon-on-insulator), there would be 1 μm of channel area. With a 10nm diameter nanowire at a 40 nm pitch, there would be 785 nm of carryingarea. With three stacked 10 nm nanowires 1002 (see FIG. 10), there wouldbe 2356 nm of current carrying area. But, with 100 nm wide stackedsheets 1604 and 1606, allowing for 28 nm between each stack of sheets,there would be 4000 nm of current carrying area. These values areillustrative and are not intended to be limiting. Other sizes may beused according to the present principles.

This increased amount of current per layout area is advantageous fordriving large loads, such as in I/O devices and power devices, andprovides the ability to modulate the amount of current generated perlayout area.

For very small dimensions, e.g., less than 6 nm, quantum confinementcomes into play, causing the ground state of the carriers to go up,resulting in a higher threshold voltage. For this range of dimensions,relaxing the confinement from 2D confinement (such as in a nanowire1002) to 1D confinement (such as in a thin sheet of silicon 1604)relaxes the quantum confinement as well, giving designers a simplevariable for fine-tuning threshold voltage in a transistor to suit theon/off current balance that is desired for each particular device intheir design.

Referring now to FIG. 17, a nanowire structure 1002 and a planar gapstructure 1602 are shown on a single chip. By employing the presentprinciples, the structures may be formed simultaneously, using a singleprocess, thereby greatly increasing design flexibility and fabricationefficiency. A gate structure 1102 is formed over and around eachstructure.

Referring now to FIG. 18, a block/flow diagram is shown for producingnanowire or double-sided gate planar FETs. Block 1702 forms verticallystacked layers of alternating channel and sacrificial material directlyon one another and onto a substrate. The substrate may be formed from,e.g., silicon oxide (SiO₂), though it is contemplated that othersubstrate materials may be used instead. A channel material, which willeventually form the nanowires, may be made from silicon, while thesacrificial material may be silicon-germanium (SiGe). It is contemplatedthat n+ or p+ SiGe may be used as a sacrificial material, though thosehaving skill in the art would be able to select any other suitablesacrificial material according to the present principles. Similarly, thechannel material is not limited to silicon, but may be formed from anysuitable substance.

Temperature budget of growth and processing should be limited to atemperature low enough to avoid inter-diffusion of separate layers. Forexample, for a Si/SiGe stack, processing temperatures should preferablyremain below 800° C. In addition to or instead of the materialsdescribed above, the following materials may be used: Ge,Si_(x)Ge_(y)C_(z), Si_(x)C_(y), and Ge_(x)C_(y), with the respectivecompounds in any appropriate proportion. This list is not intended to beexhaustive. The addition of carbon (C) can be used to increase thecritical thickness of strained SiGe or Ge layers, in addition toreducing unintentional doping of silicon interlayers. Growth pressure ispreferably kept below 50 Torr to minimize oxygen incorporation. SiGe andGe interlayers can be doped using, e.g., PH₃ or AsH₃ for an n-dopant andB₂H₆ for a p-dopant.

Block 1703 defines, patterns, and isolates the active regions of thedevice. Patterning may be done by, for example, photolithographyfollowed by reactive-ion etching (RIE). Isolation may be done, forexample, by shallow trench isolation (STI), where non-active regions arefilled with a dielectric such as SiO₂ to planarize the surface of thesubstrate, or mesa isolation, where non-active regions are simply etchedaway. Depending on whether a nanowire mesh device or a planar device isdesired, processing continues to block 1704 or block 1705. Block 1704patterns fins onto the stacked layers using a hard mask, e.g., formedwith silicon nitride. The hard mask defines the location of thenanowires along one coordinate. Block 1705 patterns a solid hardmaskthat defines in part the area for the eventual planar FETs. By selectingthe size and shape of the hardmask, one may select the size and shape ofthe resulting structures. This is not limited to wires and planes, butmay reflect any desired shape. As will be discussed below, however, if adirectional etch is used, such etching may limit the full range ofpossible shapes. Additionally, the characteristics of the etch willlimit how dense the structures may be made as well as how close togetherthey may be placed. It should also be noted that, if a chip designincludes only planar devices, the hardmask may be omitted, but that achip which includes both devices or which includes only nanowire deviceswill need to use such a mask. Block 1703 active area isolation mayalternately be done after hardmask definition.

Block 1706 forms a dummy gate over the hardmasks out of, for example, apoly-silicon or silicon nitride material stack. The dummy gate definesthe location of nanowires in another direction and also establishes theposition of eventual gates. Block 107 optionally modifies source/drainregions, which are the regions of active area not covered by the dummygate, using, any combination of spacers, implants, recess etches, and/orepitaxial growth of embedded materials. Block 1708 then fills insacrificial material (e.g., dielectric) around the dummy gate. Block1710 removes the dummy gate using, e.g., chemical etching or RIE,thereby exposing the hardmask.

Block 1712 anisotropically removes stacked material that is not coveredby the hardmask, e.g., by an RIE process. If fin hardmasks were formedin block 1704, this produces fins of stacked channel and sacrificialmaterial. If a solid hardmask was formed in block 1705, this step mayremove only the ends of active regions near the STI boundary which arenot covered by the solid hardmask. The solid hardmask of step 1705 isused to protect the layers which will form a planar device from theetching process than forms the nanowire fins.

Block 1714 removes any remaining exposed hardmask, uncovering thestacked structures left by block 1712. Block 1716 removes sacrificialmaterial from between the nanowires and the planar layerssimultaneously. Removal of sacrificial layers may be performed usingselective etching. If SiGe is used as a sacrificial layer, the removalcan be done chemically using any suitable chemical that exploits thelower oxidation potential of SiGe compared to silicon. In oneembodiment, a chemical mixture that includes one or more of hydrogenfluoride, hydrogen peroxide, and acetic acid may be employed. Forexample, HF+H₂O₂+CH₃COOH may be employed in a ratio of 1:2:3 by volume.In another embodiment, a mixture of sulfuric acid and hydrogen peroxidemay be employed using known mixture ratios to perform the etch. Dryetching may also be used with such techniques as O₂ plasma or plasmachemistries typically used for etching metals. This etching can beperformed using low temperature (e.g., less than 750° C.) wet or dryoxidation at any pressure. Hyperbaric oxidation (e.g., 10 ATM) at 650°C. shows, for example, a factor of 70 increase in oxidation rate forSiGe as compared to silicon. The layers should be kept below 800° C. tominimize interdiffusion between the SiGe and silicon layers. Suchoxidation processes can be used to oxidize SiGe while only producing athin, self-limiting interfacial oxide on the undoped silicon nanowires.This reduces gate capacitance.

For planar layers, a directionally selective etch is useful. By using anetch which preferentially removes material according to crystal faceorientation, sacrificial material may be removed from between planarlayers without affecting nearby structures. For example, etch ratesassociated along a <0 0 1> direction in SiGe layers may be ten timesgreater than etch rates along <1 1 0> directions. To perform such anetch, hydrochloric gas for example may be applied at an exemplarytemperature between 485 and 560 degrees Celsius, with highertemperatures resulting in a more rapid etch. This etch willpreferentially remove sacrificial material between planar layers withonly a small amount of “leakage” in transverse directions. Transverseetch times provide a functional limitation on directionally selectiveetching, as the etch will eventually undercut support structures or willaffect nearby devices. As such, the speed of transverse etching puts alimit on how close devices may be placed to one another.

After removing the sacrificial material from the channel region, SiGe,for example, may be used for solid-source doping of source and drainregions. This enables better vertical uniformity in junction profiles ascompared to that attainable with top-down implants. In this way, theheight of the device (the number of stacked nanowires or planes) is notlimited by an ability to define source and drain junctions from atop-down implant.

The remaining channel material is optionally doped at block 1718, and anew gate is formed at block 1720. Nanowires need not be doped but, ifso, such doping may occur before differential chemical oxidation. Solidsource diffusion annealing may be used to dope the silicon source anddrain regions and activate dopants. Differential chemical oxidation maybe used to preferentially oxidize heavily doped SiGe while forming onlyan interfacial layer on undoped silicon nanowires. Depending on theshape produced by the hardmask in blocks 1704 and 1705, this may resultin a nanowire mesh FET or in a planar FET. It is also contemplated thatother shapes may be formed according to the present principles, creatinglayered chip device structures based on hardmask patterns other thanthose shown above. Because of the shared stacked-material structure,such devices may be formed together on a single chip.

Having described preferred embodiments of double gate planar FETs andmethod for making the same (which are intended to be illustrative andnot limiting), it is noted that modifications and variations can be madeby persons skilled in the art in light of the above teachings. It istherefore to be understood that changes may be made in the particularembodiments disclosed which are within the scope of the invention asoutlined by the appended claims. Having thus described aspects of theinvention, with the details and particularity required by the patentlaws, what is claimed and desired protected by Letters Patent is setforth in the appended claims.

What is claimed is:
 1. A transistor device, comprising: a plurality ofplanar layers of channel material connecting a source region and a drainregion, wherein the planar layers are formed in a stack of layers of achannel material; and a gate conductor formed around and between theplanar layers of channel material.
 2. The transistor device of claim 1,wherein the length of the plurality of vertically aligned planar layersis greater than the width of the trench.
 3. The transistor device ofclaim 1, wherein the channel material is silicon and the second materialis silicon-germanium.
 4. The transistor device of claim 1, furthercomprising a plurality of nanowires of channel material, wherein thenanowires are formed in the stack.
 5. The transistor device of claim 1,wherein a bottom planar layer contacts gate material along a top surfaceand at least one upper planar layer contacts gate material on a top anda bottom surface.
 6. The transistor device of claim 1, wherein theplanar layers of channel material form separate channels for a singletransistor device.
 7. An integrated circuit, comprising: a planardevice, comprising: a plurality of planar layers of channel materialconnecting a source region and a drain region, wherein the planar layersare formed in a stack of layers of a channel material; and a gateconductor formed around and between the planar layers of channelmaterial; and a nanowire device, comprising: a plurality of nanowires ofchannel material connecting a source region and a drain region, whereinthe nanowires are formed in a stack of wires of the channel material;and a gate conductor formed around and between the nanowires of channelmaterial.
 8. The integrated circuit of claim 7, wherein the length ofthe plurality of vertically aligned planar layers is greater than thewidth of the trench.
 9. The integrated circuit of claim 7, wherein thechannel material is silicon and the second material issilicon-germanium.
 10. The integrated circuit of claim 7, wherein abottom planar layer contacts gate material along a top surface and atleast one upper planar layer contacts gate material on a top and abottom surface.
 11. The integrated circuit of claim 7, wherein theplanar layers of channel material form separate channels for a singletransistor device.
 12. The integrated circuit of claim 7, wherein thenanowire device comprises a plurality of stacks of nanowires formingseparate channels for a single transistor device.